ON DIMORPHOUS BODIES. 199 
Rt. Rh. Prism. Ob. Rh. Prism. Rhomboid. Cube. 
Native Sulphur, | After fusion, Iso- | When it replaces | When _isomor- 
Isomorph, with morph, with Arsenic or An- hpous with the 
Todine. Selenium.* timony. other metals. 
It is not to be disguised, however, that the reasoning in all 
these cases is at best only probable. The supposition even,—ofa 
fourth form in the case of sulphur depends on a previous one, 
that in a regular crystal of cobalt glance, arsenic can exist in the 
rhomboidal form, the only one in which it has hitherto been ob- 
served (by Breithaupt). If arsenic and antimony, like the oxides 
of the latter and the arsenious acid, be dimorphous, one of their 
forms belonging to the regular system, then the mutual replace- 
ment of these two metals and of sulphur in tessular forms, only 
strengthens the argument for the third or cubical form of sul- 
phur, which is itself also hypothetical. 
Still the facts above detailed, and we are acquainted with very 
many of an analogous kind, are deserving of much consideration. 
They open up views of great interest, and seem to indicate the 
line along which the advance of certain knowledge is destined 
to proceed. Received with caution and due distrust they will 
materially aid the observer, by teaching him what to look for 
and how to find it,—received at once as true they will at best 
form the foundation of an imperfectly verified system of opinions, 
and may probably lead to error. 
VIII. 
45. Relation of dimorphism and molecular arrangement in 
general, to temperature, electricity, and mechanical pressure. 
—Hiaving in the preceding sections exhibited nearly all the facts 
connected with dimorphism with which we are at present ac- 
quainted, it may be proper before inquiring into the cause of 
dimorphism to take a short review of the several circumstances 
by which the assumption of the one or the other form is known 
to be affected. 
Of these circumstances the influence of temperature is the Influence of 
most apparent. The various substances which have come un- *™peta- 
der our consideration as capable of existing in two forms or 
states, are almost uniformly characterized by a preference to one 
form or state in ordinary circumstances or at ordinary tempe- 
* Sublimed and crystallized from its solution in sulphuric acid (Frankenheim) 
Pog. Annalen, vol. xl. p. 459. 
